Agreed, while a Pentium g3258 is good for a budget build, pairing it with such a high-end video card would be overkill and wastefull. However, I believe you are talking about upgrading the graphics card later. If so then you'll presumably also be upgrading the processor.
If you are going to do the build
Pentium g3258
H81 motherboard
Radeon 270x
4-8gbs ram
Then upgrade components over time
Switch processor for I5, upgrade to 780ti(or whatever you choose at the time)
Then this is a great solution as it allows you to swap in better components without changing the entire system. (Mobo/Ram/etc) and you can always throw used parts on ebay and make back a good majority of your money like that.
So if the plan is to upgrade over time Awesome, however if not then I would suggest considering some more mid-range options.
CPU: Intel Core i5-4430 3.0GHz Quad-Core Processor ($172.98 @ SuperBiiz)
Motherboard: MSI H81M-P33 Micro ATX LGA1150 Motherboard ($49.98 @ OutletPC)
Memory: Corsair XMS 8GB (1 x 8GB) DDR3-1600 Memory ($69.99 @ Newegg)
Storage: Samsung 840 EVO 120GB 2.5" Solid State Drive ($84.99 @ NCIX US)
Video Card: Asus GeForce GTX 770 2GB DirectCU II Video Card ($309.99 @ NCIX US)
Power Supply: Corsair Builder 600W 80+ Bronze Certified ATX Power Supply ($34.99 @ Newegg)
Total: $722.92
Plus case and things of that nature.
Of course as I said if you plan to just build something to upgrade in the future.
The pentium with an h81 board and the 270x you mentioned earlier will be a great starting point.